Hey,

The answer to you question is a big Yes. You can change your stream while studying in Class 11 th from Commerce to Science stream. But once if you passed your 11 th in one stream you won't be able to switch to science.

To be more precise about the other procedure I will suggest you to contact your  school. Only they can help you with this switch process as they are the ones who register students to the respective board. You should contact you admission heads for more help regarding this. They will surely help you with this.

Hope that helps.

Thank you